Electronic discharge device of the cavity resonator type



'"iled April 19, 1944 4 Sheets-Sheet l 1 1 L 1 I I Z7 A7 I1; II m EH6 26Q l-% 27 H Sept. 16, 1952 b. M. POWERS 2,611,110

ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE fink/Hal flaw/0 M fbwms,

.20 w/fg Sept. 16, 1952 D. M. POWERS 2,

ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Filed A ril 19,1944 4 Sheets-Sheet 2 a6 a 7 Z 1 26 a6 a7 36 UI'IHI" 29 32 I I I I 1 1 1r I 1 1 1 1 r //l t A 7"0/f.

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ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Filed April 19,1944 D. M. POWERS Sept. 16, 1952 4 SheetsSheet 5 D. M. POWERS Sept. 16,1952 ELECTRONIC DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE FiledApril 19, 1944 4 Sheets-Sheet 4 Maw/mt. fio/mw M fflmr/ra, M1,

Patented Sept. 16, 1952 ELECTRONIC DISCHARGE DEVICE OFI'IIHE Y CAVITYRESONATOR TYPE Donald M. Powers, Boston, Mass., assignor to RaytheonManufacturing Company, Newton, Mass, a-corporation of DelawareApplication April 19, 1944, Serial No. 532,012

9 Claims. 1

This invention relates to .a magnetron oscillator of .the plural-anodecavity type which is adapted to generate oscillations of hyper-frequency.having wave lengths of the order of a few centimeters or less. In suchdevices the wave length which is generated is dependent upon thegeometricalsize of each anode cavity, and thus for their short wavelengths the anode cavities must be made correspondingly small. Theamount of power which each cavity can generate is correspondinglylimited. Thus in a magnetron'in which the usual number of anode cavitiesexists, the power-which such a magnetroncan deliver is comparativelylow. Attempts to increase the amount of power which such a device candevelop by increasing the number of the anode cavities have heretoforeintroduced considerable difficulties. For example, such a device tendsto generate various spurious oscillations with a resulting decrease inefficiency. Likewise the effectiveness of anode cavities remote from theoutput coupling device decreases so that in some instances such anodecavities contribute -very little, if anything, to the power supplied'by'the device.

An-object of this 'inventionis to devise a magnetron oscillator-whichis-capable of generating substantially increased amounts of power ofshortwave lengths.

Another .object is to devise such a magnetron in which the e'fiiciencyand eiiectiveness of the device as a whole is substantially increased.

A furth'er object is to provide such a magnetron with-a comparativelylarge number of anode cavities, together with a common cavity resonatorinto which energy is :fed from a plurality of points on the anodestructure.

Astill further :object is to devise an arrangement whereby .the:cavityresonator may be adjusted .to .provideifcr a substantial maximumof coupling "efiiciencywith the oscillating portions of the amagnetron,:and :also to provide means therein whereby :tuning .of :the entiredevice :may be accomplished through a significant range.

The-foregoing and .other objects of this invention will be bestunderstood from'the following description of exempliiications thereof,reference being had to the accompanying drawings wherein:

Fig. -1 is a vertical cross-section of one embodiment of my inventiontaken along line I*! of Fig.2.;

Fig. 2is a transverse crossesection "taken-alon line? +2 of Fig. 1;

' thermionic,

.2 Fig. 3 is a. view similar to Fig. 1 of another embodiment of myinvention taken along line 33 of Fig. .4;

Fig. 4 is a cross-section taken along. line 4-6 of Fig.3; and

Fig. 5 is a.diagrammaticillustration.ofa cavity resonator.

The magnetron illustrated in Figs. .1 and -2 comprises a tubular anodestructure I! made. of a cylinder of conducting material, such as -.cop'per. A plurality of radially-disposed plates .2 likewise formed of aconducting material, such as copper, are soldered in place along theinner surface of the hollow cylinder .1. Each pair of plates, togetherwith the intervening portion of the cylinder I, define .anoscillatorycavity. Each of these cavitiesis small enough to generateoscillations ofthe desired short wave length. Although each of these cavitiesiscapableof generating a comparatively small amount of power,

there are provided a comparatively large .number of radial plates 2 andthus acomparatively large number of said cavities in order that thetotal power of the .device may reach acomparatively high value.

The inner ends of the radial, plates 2, are adapted to serve as .anodefaces ,for receiving electrons emitted from the centrally locatedcathode 3. This cathode is preferably of the indirectly-heated,oxide-coated type having an interior heater .4 and an outer cathodesleeve '5 coated on its exterior surface with suitable electron-emittingoxides. Alternate plates 2 are preferably electrically "connected bymeans of conducting straps "1, 8., 9 and H3. The straps 1 and 8 arelocatedat one end of the anode structure, the strap 1 being electricallyconnected to the alternate plates 2, while the strap 8 is connected tothe intervening alternate plates. At the other end of the anodestructure the strap 9 is connected .to those plates to which the strap'8 is connected, and the strap i0 is connected tothose plates to whichthestrap I is-connected. Such a'strap'arrangement decreases the tendencyfor the device to operate in various spurious modes, and reinforces thetendency of the tubes to oscillate in theprimary desired mode.

The energy developed within the oscillating cavities or chambers isadaptedto feed into a common cavity resonator N. This cavity resonatoris formed by thespace between the cylindrical'member l and an-outercylindrical wall The interior I I into a choke coupler device 29.

of the device is hermetically sealed by upper and lower cap members I3and I4 hermetically soldered in place at the upper and lower ends,respectively, of the cylindrical members I and I2. A pair of upper andlower magnetic pole pieces I5 and I6 are set into and hermeticallysoldered in openings in the upper and lower cap members I3 and I4,respectively, thus completing the hermetically-sealed enclosure. Themagnetic pole pieces I5 and I6 may be energized with a magnetic fieldsupplied from an external electromagnet or permanent magnet in a manneras shown and described in the copending application of William C. Brown,Serial No. 503,622, filed September 24, 1943, and now U. S. Patent No.2,416,899. In order to support the cathode 3 within thehermetically-sealed enclosure, said cathode is mounted at the upper endof a hollow conducting tube I? electrically connected to the cathodesleeve 5. Said hollow tube extends through an opening I 8 "formed in themagnet pole I6. The tube II is carried by the upper end of a hollowconducting rod I9; The upper end of the heater 4 is electricallyconnected to the cathode sleeve 5, while the lower end of said heater isconnected to a conductor which extends through the tube II and thehollow rod IS, and passes out through a glass seal 2! carried at thelower end of the hollow rod I9. A metal sealing sleeve 22 is set intoand soldered in place in an enlarged opening 23 formed in the pole pieceI6 and communicating with the opening I8. One end of a glass tube 24 issealed to the lower end of the sealing sleeve 22. The other end of saidglass tube is sealed to a sealing cup 25 connected to and hermeticallyjoined with the lower end of the hollow rod I9. By the above arrangementthe cup 25 serves as the external electrical connection for the cathode,and the cup 25 together with the conductor 20 serve as the externalelectrical connections to the heater 4. v

In order that the energy developed by the oscillating chambers formed bythe anode plates 2 may be fed into the cavity resonator I I, couplingslots 25 are formed through the wall of the cylindrical member I andconnect a predetermined number of oscillating chambers disposed aroundthe anode structure with the cavity resonator I I. In order that theimpedance of the oscillating anode structure may be matched to theimpedance of the cavity resonator, the slots 26 are formed as impedancetransformers. For this purpose each slot 23 has a greater length lookinginto the oscillating anode structure, and a smaller 4 length lookinginto the cavity resonator I I. This provides an impedance transformingdiscontinuity 21 within the slot 26. By proper dimension ing, thedesired impedance matching may be secured. The energy delivered to thecavity resonator II may be led out to a suitable utilization device by aproper output coupling arrangement. In the present embodiment thecylindrical member I2 is provided with an elongated slot 28, the narrowdimension of said slot appearing in Fig. 2. Said slot feeds energy fromthe cavity resonator This choke coupler consists of a hollow tubularconducting member 3!] hermetically soldered in place on the externalwall of the cylindrical member I2. The member 30 may be provided with acentral passage SI serving as a hollow Wave guide. The outer end of themember 33 may be provided with a suitable quarter-wave length choke slot32. In order to complete the hermetic seal of the device,

a glass member 33 is sealed across the open end of the member 30. Ahollow wave guide 34 presented to the end of the member 39, as shown inFig. 2, will be properly coupled to the device in such a manner thatsaid hollow wave guide 34 will be energized to feed energy from theoscillating tube to a suitable external consumption device. If furtherimpedance matching is desired so as to eliminate reflection within thechoke coupler 29, a conducting inset 35 may be inserted in the opening3i so as to provide an impedance transforming discontinuity therein.

In order that the energy supplied through all of the slots 26 shallcombine with maximum effectiveness in the cavity resonator I I, thelocation of said slots 23 as they enter the cavity resonator I I must bematched to the pattern of waves as established in said cavity resonator.In other words, each slot 26 is preferably located at maximum of thestanding wave created in the cavity resonator, and should be in theproper phase relation with respect thereto so as to reinforce said wave.In order to satisfy the above requirements, the distance along thecavity resonator between adjacent slots 26 should satisfy the followingrelationship:

(Equation 1) where m is any whole number and Ag is the wave length ofthe Wave within the cavity resonator II. If adjacent slots 26communicate with oscillating anode chambers which are in time phase witheach other, then 114 should be an even numher, while if adjacent slots26 communicate with anode cavities which are substantially 180 out oftime phase with each other, then 111 should be an odd number.

If cavity resonator I I were provided in a completely toroidal form withno ends thereto, the location of the slots 26 in accordance with theabove relationships would automatically establish the locations of themaxima of the standing wave within the cavity resonator. Under suchconditions it might be diflicult to design a structure in which therelationships as described above are satisfied to a maximum degree, andtherefore with a resultant maximum of efiiciency of the device. It istherefore desirable that means be provided for securing some degree ofadjustment of the wave pattern within the cavity resonator II for thepurpose of matching said pattern to the locations of the slots 26. Forthis purpose the cavity resonator II is provided with terminal plates 36and 31 formed of conducting material extending across and substantiallycompletely closing the cross-sectional area of the cavity resonator. Theposition of the plates 36 and 31 may be adjusted by links 38 and 39pivoted to the backs of said plates, respectively. Both links 38 and 33are also pivoted to the lower end of an adjusting rod 43. The adjustingrod 43 is carried by the lower end of a hermetically-tight bellows 4|sealed in the walls of a tubular housing 42, the lower end of which ishermetically sealed and may be provided with a knurled edge for readyrotation and adjustment of the screw 43. By rotating the adjusting plate44, the rod 40 is moved longitudinally, thus adjusting the posiacrmrotions of the. plates 36'andf 37. In. order to guide the. plates 36, and31; in. their. motion, the. plate 3.6. may be" provided. with a curvedrod 316 fitting into a. correspondingly curved sleeve. 37" carried bythe plate 31.;

Since the deviceas described; above. is, capable of generating and.delivering large amounts. of power,, it may be desirable. to provide.means for coolingthe device. For. thispurpose holes 45 may be.drilledfllongitudinally throughthe walls of. the cylindrical member. I.These holes teed.v into common passages 46 and 4.1 at the. upper. andlower ends respectively or said cylindrical memberv I'.. Pipes. 48 and49. may. be. connected to the structure for supplying and. carryingawaythe necessary cooling fluid'.. In this way, acooling medium, such as.water. or air, may be. supplied to the device. to keep" its. temperaturewithin reasonableliinits.

The cavity resonator. H is substantially equivalent toa. cavityresonator having. the simple form. asillustrated. in Fig. 5..Thislcavity resonator has .a length] andialtransverse. dimension 17. Theequations relating the dimensions b and l, the free, space wave length.and. the wave. length. Xg within the cavity. resonator. are

I (Equation 2') where. n. an. integer. Also c" A Where c' issubstantially the velocity of light, and f is the frequency of" theoscillations generated within the anode structureof the tube..

In order that the. conditions of Equation 1 shall be satisfied, Xgshould have. a. particular length dependent upon the spacing between.the slots 26. From Equation 3 wesee that the value of M7 maybe adjustedby varying 1; Such a variation is provided by the. adjustment of thepositions of theplates 36 and 31, as described above, between thesurfaces of said plates through the cavityresonaton.

Since the plates 35 and 31 are formed of conducting material, itisclearthat the wave pattern set up-within the cavity'resonator it will haveminima at saidplates. We have already seen from the above discussionthat the distance between said plates through the cavity resonator H isequal to an integral. number of halfwave lengths. Therefore, thelocation of the" plates 35 and. 3? also establishes'the positions of themaxima of the wave within the. cavity resonator; Thusa shifting of the.plates 32 and 3?: a unit around the wave guide will. shift the entirepat ternrofzthezwavetherein, sothatmaxima of said wave may occurattheslots 26. Such a matching of: the. maxima: with the slots: 26 maybe accomplished bypredetermining. the position of the pair of plates. 36and 3.1 in the. initial constructionot the. tube- Also a certain: degreeof adjustment can. be secured. by bending the ad justing: screw. 432 soas to displace the plates 3%: and 31' to oneside or-the other of the ofthe housing 42;

Since the dimension D- appearingin Equation 2 is fixed by thedistancebetween the inner sur faces of the caps l3 and Hi, we see fromsaid (Equation) 6 equation thatithe value of'lig; as called; iorbytheadjustment .011 the plates 36' and 31,.wi1l-i'nturn require aparticularvalue ofx," and thus a particular value'of as requiredbyllquation 4; For maximum effectiveness; therefore, the anode structureshould be designed so that iii-normally tends to oscillate at suchafrequency. If, however; theirequency at which the: anode normally tendsto oscillate difiers somewhat from the frequency. as. required bylthevadjustment: of the plates. 35' and; 31, the cavity; resonator M willreflect asuincient" amount ofireactive impedance into. the oscillatinganodastructure to pull the frequency. thereof, into' agreement" with thefre-- quency calledlfor' by the value ofil resulting from the.positioning of the plates 36 and, 31. However, for maximumeffectivenessit' is desirable that the normal. frequency'of the anodestructure should agree withv the-frequency, as required by that valueof. l inwhich the wave pattern within, the cavityresonator I t ismatched to the positions of" the slots 26;

A certain degree of tuning or variation in the frequency" of theoscillator may be secured by adjustment of the: positions of the plates38 and 31. A variation irrl. varies Ag; and fromEquation 2: we see thatwith a. fixed value of 5; such a variation should produce a variation-inR. However; attempts to vary' the positions of the plates 36 and 31 awayfrom a conditionin which the wave pattern in thecavity resonator: ii ismatched with the positioned the slots 25 will decrease theefiectiven'ess of" the transfer of energy from. the anode structure to;the cavity resonator. 'I'hus only a comparatively slight degreeof thistype-of tuning canbe tolerated in the tube:

If it' i's desired t'o'secure a greater degree of tuning and flexibilityof adjustment than: that possible with the embodiment asdescribedzabove, the arrangementas shown-in Figs. 3; and. 4. may beutilized. In: these: figures the samereferen'ce numerals. which appearin. Figs. 1 and 2. areapplied where the el'ementsare. identical. In thearrangementasshownjinFigszBand 4 the commoncavity'resonator:isformed asa chamber 53 formed by the spacesv between the cylindrical member and.theeouterscylindrical wall member 5| formed of a. suitable conducting;material. The cylindrical wall member 5|eXtends-to'substantially'beyondithe. upper end of.' the cylinder 1, andis hermetically sealed by a cap 52* hermetically soldered in place inthe top of said cylinder 51.. The. cap 52- has a central openinga'crcssswhichis sealed a flexible: diaphragm 53. The;di'aphragm1 53 has.rigidly secured to its center a rod. 54. which carries a, tuning member55; at. its lower end, This tuning member is formed; of conducting;material having a lower ring;-shap e d surface. 56; whichfits into theannular: spacebetween. the'members I. and 5.! and defines the uppers-urface'of the cavity resonator 5.0: The upper end of. the cylindricalmember i may: be. closed bya cap 51- soldered in. place thereon. In.order to adjust. thepositionof the surface-56, the;diaphragm 53 hassecured. to the center thereofathreaded. stub 58. extending outwardlyfrom.thedevice. The stub. 58 is received in a. threaded. hub 59 of anadjusting p-l'atefit. l'he hub, 5.! is.rotatably mountedjin the covermember 61' bolted onto. the. cap 52. The. adjustingplate. 60. preferablyextends beyond. the edges ofthecovermember 6| andis knurled so. as toprovide for. a ready rotation of said plate with the consequentadjustment of the position of the surface 56; An upper pole piece 62maybe placed 7 adjacent the upper end of the structure cooperating withthe pole piece It to create a magnetic field within the device, asdescribed in connection with the pole pieces l5 and iii of Fig. 1.

Instead of coupling the oscillating chambers within the anode structureto the cavity resonator 50 by means of slots, the alternativearrangement as shown in Figs. 3 and 4 may be utilized. In thisarrangement a coupling loop 63 is placed in each of certain anodechambers.

One end of the coupling loop is mechanically and electrically connectedto the inner wall of the cylinder l. The other end of the coupling loopextends out through openings in the cylindrical member I into the cavityresonator 50 so as to form probes 64 therein. The relationship of theprobes 54 to the cavity resonator 50 should be substantially asdescribed in connection with the relationship between the slots 26 inthe cavity resonator H of Figs. 1 and 2.

Instead of using the type of output coupling as described in connectionwith the previous embodiment, this second embodiment may be providedwith an alternative output coupling arrangement, as shown in Fig. 4. Inthis arrangement a probe 65 formed as the extension of a conductor 66extends into the cavity resonator 50. The conductor 58 extends throughpipe 6"! and passes out through a glass seal 63 carried by the outer endof said pipe. The pipe 6'! is likewise hermetically sealed in the wallof the cylindrical member 5|. An additional hollow conducting pipeconnected to the pipe 81 may surround the conductor 66 so as to form aconcentric transmission line through which the energy may be led to asuitable utilization device. The probe 85 should be located at a maximumpoint on the standing wave within the cavity resonator 50 so as toreceive a maximum amount of energization.

When the device as described above is energized, oscillations will begenerated in the anode structure, will pass by means of the probes 64 inthe cavity resonator 50, and will be led out through the concentrictransmission line, including the conductor 66. Since the tuning surface56 must be free to move up and down in the annular space between thecylinders I and 5| for tuning purposes, there will necessarily be asmall space between the walls of these cylinders and the side walls ofthe depending annular portion of the tuning member 55. However, therewill be very little tendency for any of the high frequency energy to bepropagated through these spaces. members, a relatively high capacitywill exist across the above-mentioned gaps. This high capacity willpresent a relatively low impedance to the hyper-frequency energy, andthus will substantially short-circuit the gaps. In order to insureagainst the loss of any hyper-frequency energy through the gaps, thewalls of the depending annular portion of the tuning member 55 may beprovided with quarter-wave length choke slots extending around theentire circumference of the outer and inner gaps existing between themember 55 and the cylindrical members El and I, respectively. Thesechoke slots therefore present a low series impedance so as to assist inthe short-circuiting of the gaps.

The cavity resonator 50 is again equivalent to the cavity resonator asdiagrammatically illustrated in Fig. 5, and the Equations 1-4 apply withequal force. In the case of this latter embodiment, the adjustablesurface 56 enables the di- Due to the close spacing between thesemension b to be varied, while the plates 36 and 3'! enables thedimension Z to be varied.

If we now adjust I so as to match the wave pattern in the cavityresonator 50 to the position of the probes 64 and with a given value ofb, the normal frequency of oscillation of the anode structure produces avalue of A which does not satisfy Equation 2, the value of b can beadjusted until said equation is satisfied. In this way the system canalways be adjusted to a point of maximum efliciency since the anodestructure can be permitted to oscillate at its normal unrestrainedfrequency.

If it is desired to tune the frequency of the device, such a tuningarrangement is also possible. For this purpose the value of l is fixedby the position of the plates 36 and 31 so as to produce the desiredmatching of the wave pattern with the positions of the probes 64. Thislikewise fixes the value of Ag. If new the tuning surface 56 is variedso as to change the value of b, it will be noted that Equation 2 willrequire a corresponding change in the value of x. This will require acorresponding change in the value of f pursuant to Equation 4. Underthese conditions the cavity resonator 50 will re fleet a sumcient amountof reactive impedance into the oscillating anode structure to pull thefrequency thereof into accord with the frequency called for by theadjustment of the tuning surface 56. It will be noted, however, thatsuch a tuning adjustment does not disturb the matching of the wavepattern within the cavity resonator to the position of the probestherein.

Of course it is to be understood that this invention is not limited tothe particular details as described above as many equivalents willsuggest themselves to those skilled in the art. It is accordinglydesired that the appended claims be given a broad interpretationcommensurate with the scope of the invention within the art.

What is claimed is:

1. A high frequency oscillator comprising an electron discharge tubehaving a plurality of oscillatory chambers therein, a cavity resonatoradapted to be excited by said oscillatory chambers, a plurality of saidoscillatory chambers being coupled directly to said cavity resonator ata plurality of points spaced along the length of said cavity resonator,said resonator incorporating adjustable means for shifting the positionof the standing wave pattern established therein by said excitation,said resonator having a substantially rectangular cross-section with adimension axially of said resonator greater than the Width thereof, andmeans coupled to said resonator for adjusting said axial dimension fortuning said oscillator.

2. A high frequency oscillator comprising an electron discharge tubehaving a plurality of oscillatory chambers therein, a cavity resonatoradapted to be excited by said oscillatory chambers, said resonatorhaving a pair of closed ends defining a predetermined length of saidresonator, a plurality of said oscillatory chambers being coupleddirectly to said cavity resonator at a plurality of points spaced alongsaid length of cavity resonator, means in said resonator for adjustingthe position of said ends relative to each other for adjusting saidlength, said resonator having a substantially rectangular crosssectionwith a dimension axially of said resonator greater than the widththereof, and means coupled to said resonator for adjusting said axialdimension for tuning said oscillator.

3. A high frequency oscillator comprising an electron discharge tubehaving a plurality of oscillatory chambers therein, a cavity resonatoradapted to be excited by said oscillatory chambers, said resonatorhaving a pair of closed ends defining a predetermined length l of saidresonator, I being substantially equal to where n is a whole number andmg is the wave length of the radiations in said cavity resonator, aplurality of said oscillatory chambers being coupled directly to saidcavity resonator at a plurality of points spaced along said length ofcavity resonator, and separated from each other by a distance of where mis a whole number, said resonator incorporating means for adjusting theposition of said ends relative to each other for adjusting said lengthZ, said resonator having a substantially rectangular cross-section witha dimension axially of said resonator greater than the width thereof,and means coupled to said resonator for adjusting said axial dimensionfor tuning said oscillator.

4. A high frequency oscillator comprising an electron-discharge devicehaving a plurality of oscillatory chambers therein, and a cavityresonator adapted to be excited by said oscillatory chambers, aplurality of said oscillatory chambers being coupled directly to saidcavity resonator, and said cavity resonator being provided withadjustable means for shifting the position of the pattern of thestanding wave established therein by said excitation, whereby selectedpoints along the length of said pattern may be selectively located withrespect to the points of coupling between said oscillatory chambers andsaid cavity resonator.

5. A high frequency oscillator comprising an electron-discharge having aplurality of oscillatory chambers therein, and a cavity resonatoradapted to be excited by said oscillatory chambers, a plurality of saidoscillatory chambers being coupled directly to said cavity resonator atpoints spaced from each other by a distance where n1 is a whole numberand 1g is the wave length of the oscillations in said cavity resonator,said cavity resonator being provided with adjustable means for alteringthe electrical length Z thereof such that the position of the patternstructure; an anode structure, spaced from said cathode structure, andprovided with a plurality of oscillatory chambers therein; a cavityresonator surrounding said oscillatory chambers and being coupled toselected ones thereof, whereby said oscillatory chambers excite saidcavity resonator; and means extending into said cavity resonator forshifting the position of the pattern of the standing wave establishedtherein by said excitation, whereby predetermined points along thelength of said pattern are matched to points of coupling between saidoscillatory chambers and said cavity resonator.

7. In an electron-discharge device: a cathode structure; an anodestructure, spaced from said cathode structure, and provided with aplurality of oscillatory chambers therein; a cavity resonatorsurrounding said oscillatory chambers and being coupled to selected onesthereof, whereby said oscillatory chambers excite said cavity resonator;and a pair of coacting shorting plates movable in said cavity resonatorfor shifting the position of the pattern of the standing waveestablished therein by said excitation, whereby predetermined pointsalong the length of said pattern are matched to points of couplingbetween said oscillatory chambers and said cavity resonator.

8. An electric discharge device comprising a substantially cylindricalenvelope having an open end, a space resonant anode structure supportedwithin said envelope, a structure for tuning said anode comprising ahollow metallic cylinder having an apertured end wall for the receptionof a portion of said space resonant anode, and a flexible vacuum-tightconnection between a second wall of said tuning structure and saidenvelope.

9. An electric discharge device comprising a substantially cylindricalenvelope having an open end, a space resonant anode structure supportedwithin said envelope, a structure for tuning said anode comprising ahollow metallic cylinder having an apertured end wall for the receptionof a portion of said space resonant anode, and meansv connected withsaid tuning structure for producing relative movement between said anodestructure and said tuning structure.

DONALD M. POWERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,190,668 Llewellyn Feb. 20, 19402,247,077 Blewett et al June 24, 1941 2,261,130 Applegate Nov. 4, 19412,280,824 Hansen et al Apr. 28, 1942 2,284,405 McArthur May 26, 19422,404,261 Whinnery July 16, 1946 2,409,640 Moles Oct. 22, 1946 2,411,953Brown Dec. 3, 1946 2,419,172 Smith Apr. 15, 1947 FOREIGN PATENTS NumberCountry Date 509,102 Great Britain July 11, 1939

